Write the purpose of a sentence on the board for kids to examine. A sentence is a group of words that makes a statement or asks a question. Discuss with kids what an opening sentence should accomplish. The main goal is to encourage readers to want to read the next sentence. This can be accomplished by asking a question readers want answered or presenting an idea that promotes curiosity.
Write the requirements of a sentence for students to use as a guideline when constructing he sentence examples. The simple sentence must have a subject and an object. Explain the subject is typically doing something to the object. Explain that doing something is the verb portion of a sentence.
Read a selection of opening sentences from books children are familiar with, or ask students to bring in their favorite books. Discuss the opening sentence and ask students to describe what each of those sentences told them about the story or how the sentence made them want to continue reading.
Describe a situation to students and challenge them to use the subject and object, along with a verb, to create an opening sentence as if they were going to relate the situation you described in story form.
Write examples of a good opening sentence on the chalkboard. For instance write, "Jackie found a mysterious package on her doorstep and brought it into the house." Discuss with students how this sentence accomplishes one of the purposes discussed. Encourage students to write a paragraph based around that opening sentence and compare what they come up with to see how an opening sentence can suggest different things to different people.
Write the end of a sentence on the chalkboard. An example sentence ending might be, "...a snarling dog with big teeth." Ask students to write the first part of the sentence.